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ubiquitin (UBCEP2, UBB, UBC)

A non-histone high mobility group protein found in chromatin. Function: - derived from cleavage of ribosomal protein S27A - adenylate cyclase stimulating polypeptide - covalently attached to target proteins by a multienzymatic system consisting of: a) ubiquitin-activating enzyme E1 b) ubiquitin-conjugating enzyme E2 c) ubiquitin-ligating enzyme E3 - ubiquitin is attached to Lys on the target protein as a monomer or as a Lys-linked polymer - the 26S proteasome is involved in ubiquitin-mediated degradation of proteins - attachment to proteins as a Lys-48-linked polymer usually leads to their degradation by proteasome - attachment to proteins as a Lys-63-linked polymer usually does NOT lead to their degradation, but are rather plays a role in signaling cellular stress - single chain of at least 4 ubiquitin residues attached to a single Lys is necessary for ubiquitin-mediated proteolysis - attachment to proteins as a monomer or as an alternatively linked polymer does not lead to proteasomal degradation & may be required for numerous functions, including a) maintenance of chromatin structure b) regulation of gene expression c) stress response d) ribosome biogenesis e) DNA repair - several types of polymeric chains can be formed, depending on the Lys used for the assembly Structure: - the last four C-terminal residues (Leu-Arg-Gly-Gly) extending from the compact structure of ubiquitin to form a 'tail' involved in covalent conjugation of ubiquitin to target proteins - ubiquitin conjugation occurs through an isopeptide linkage between the C-terminal Gly of ubiquitin & the epsilon amino group of Lys in the target proteins - ubiquitin is synthesized as a polyubiquitin precursor with exact head to tail repeats - belongs to the ubiquitin family Compartment: cytoplasm, nucleus Comparative biology: - believed to be universal in all living cells - the number of repeats differ between species & strains - in some species there is a final amino-acid after the last repeat, here in human a Val - some ubiquitin genes contain a single copy of ubiquitin fused to a ribosomal protein (either L40 or S27a)

Related

26S proteasome E3 ubiquitin ligase; ubiquitin-ligating enzyme E3; N end-recognizing protein ubiquitin Ag in tissue ubiquitin C-terminal hydrolase; UCH; ubiquitin thiolesterase; ubiquitin-specific processing protease; deubiquitinating enzyme ubiquitin-activating enzyme E1 (ubiquitin-like modifier-activating enzyme 1, A1S9 protein, UBE1, UBA1, A1S9T) ubiquitin-conjugating protein E2 (ubiquitin carrier protein)

Specific

polyubiquitin-B; contains: ubiquitin (UBB) polyubiquitin-C; contains: ubiquitin (UBC)

General

high-mobility group [HMG] protein

Properties

SIZE: MW = 9 kD entity length = 76 aa COMPARTMENT: cell nucleus cytoplasm MOTIF: ubiquitin domain MOTIF: lysine residue {K48} binding site SITE: 54-54 FOR-BINDING-OF: ubiquitin-activating enzyme Ser phosphorylation site {S57} Ser phosphorylation site {S65} histidine residue {68} binding site SITE: 72-72 FOR-BINDING-OF: ubiquitin-activating enzyme binding site SITE: 76-76 FOR-BINDING-OF: protein :QUALITIES Acceptor

Database Correlations

OMIM correlations SWISS-PROT correlations Pfam PF00240 LOCUS-LINK correlations KEGG correlations

References

  1. Pickart CM. Ubiquitin in chains. Trends Biochem Sci. 2000 Nov;25(11):544-8. Review. PMID: 11084366
  2. Pickart CM, Eddins MJ. Ubiquitin: structures, functions, mechanisms. Biochim Biophys Acta. 2004 Nov 29;1695(1-3):55-72. PMID: 15571809
  3. UniProt :accession P62988